Production of aliphatic acids



Patented May 26, 1942 Henry Dreyfus,

London,

and Walter Henry Groombridge, Spondon, near Derby, England, assignors toGelanese Corporation of America, a corporation of Delaware p No Drawing.Original application March '22,

1939, Serial No. 263,420. Divided and this application December 7, 1940,Serial No. 369,11

In Great Britain April 1, 1938 11 Claims.

This invention relates to the production of fatty acids from theirsalts. This application is adivisional of our application Ser. No.263,420 filed March 22, 1939. v I

7 According to the invention carbon dioxide and ammonia are brought intocontact with a solution of a metal salt of a fatty acid, so as toform-the ammonium saltof the fatty acid from which the free acid mayreadily be obtained. For example, this may be done by the methodsdescribed in U. S. Patents Nos. 2,090,941 and 2,090,947. Since themethod of U. S. Patent No. 2,090,947 depends on the presence of metalsalts of the fatty acids, it is of particular value when not all of themetal salt has been decomposed by the carbon dioxide.

The reaction between carbon dioxide, ammonia and sodium acetate, forexample, results in the precipitation of sodium bicarbonate and theformation of ammonium acetate. The solution so obtained may be freedfrom sodium bi-' carbonate, for'example .by decantation, filtra- Itionor centrifuging, preferably in the cold, and may then be treated torecover aceticacid from the ammonium acetate. acetate may be returned tothe process. Potassium acetate may b'e1treated similarly.

The solvent for the metal salt of the fatty acid should be chosen withreference to the particular metal and fatty acid contained in the salt,as well as the corresponding ammonium sa1t,.is more soluble in thesolvent than isthebicarbonate of the metal. i

. Aqueous solutions of the acetates or other lower fatty acid salts ofalkali metals may be used, as may also solutions in lower aliphaticalcohols, for example methyl, isopropyl, or especially ethyl alcohol.Preferably a relatively con centrated alcohol is used. For example whenusing ethylalcohol it, is preferable to employ'a concentration of atleast-85% and preferably higher, e. g. 90-98% especially about 94 Byemploying high concentrations full advantage can be taken of theinsolubility of the bicarbonates in alcohols. V Y

The rate of reaction may be increased by employing the carbon dioxide inas high concentration as possible. Thus it is, advisable always to havethe solution saturated with the gas, and advantageously excess of thegas may be passed through the solution and recirculated.

The concentration of the carbon dioxide may also be increased to avaluable degree by working under a pressure higher, and preferablyconsiderably higher, than atmospheric; preferably Unchanged sodiumvertical towers or other vessels, up which a a pressure above 70 lbs/sq.inch is used., e. g. a pressure of 80, 100, 120 or 150 lbs/sq. inch. Ifdesired still higher pressures, e. g. 200, 400 or 800 lbs/sq. inch maybe used. The temperature employed may be atmospheric, but it isadvisable to employ higher temperaturea'for example 70 -l30 C. Oneadvantage of using such higher temperatures is that the bicarbonates arethen precipitated in a form which is' more readily removed byfiltration.

The concentration of the metal acetate in the solution is preferably ashigh as is conveniently possible. When treating sodium acetate in solution in alcohol, it is preferred to employ substantially saturatedsolutions.

The process can be carried out as a batch process inone or moreautoclaves, or it may be carried out continuously. For example, thesolution saturated with ammonia may be passed downwards through asuccession of substantially stream of carbondioxide is passed,preferably under pressure as already indicated. If the solution is drawnofi at a point near but not at the bottom of each tower a considerablepart of the precipitated bicarbonate can be collected in the spacebetween the draw-off and the bottom of the tower, this space thusforming a settling compartment for the precipitate. .Ihe settlingcompartment, which may with advantage be wider than the body of thetower, may

be provided above and below with suitable valves or cocks, so that whena considerable amount of precipitate has collected this may be drawnoff, together with the solution in the lower end sure employed in theprocess, and this carbon dioxide returned to the fatty acid saltsolution. The carbonate remaining may if desired ,be converted into thecorresponding hydroxide.

The invention is thus of particular interest in the saponification' ofcellulose acetate textile materials with caustic soda 'or potash, sinceit provides a simple and cheap cyclic process whereby substantially allthe sodium or potassium base can be regenerated for re-use, and theacetic acid removed from the materials can be recovered. If desiredsodium acetate may be converted into potassium acetate before thetreatment, so as to make use of the greater solubility of potassiumacetate in aqueous alcohol.

For example, potassium. chloride may be. added 10..

to "an alcoholic solution of sodium acetate, whereby sodium chloride isprecipitated, leaving potassium acetate in the solution; the propor tionof sodium precipitated as chloride may be increased by evaporting ofl'alcohol, preferably until a saturated solution of potassium acetate 7remains The following examples illustrate without in any way limitingthe invention,

Example 1 A saturated solution of sodium acetate in 94% ethyl alcohol inan autoclave is'first saturated with" ammonia under 200' lbs. 'persquare inch pressure, 'and. is then subjected "to the action of carbondioxide under a partial pressure of 215 lbs. per square. inchlat 100 C.After-about 2' hours the pressureisfreleased; the solution containingammonium acetate is allowed to cool; and

then separated by filtration from the precipitated sodium bicarbonate.

To recover free'acetic' 'a'cid this solution 1s heated in a stillprovided with a fractionating column. Asthe temperature risesconsiderable quantities of ammonia come over, and may be collected, andincreasing quantities of alcohol also distil over. The heating iscontinueduntil the temperature in the still reaches 140 0.; the recoveryof-the 'acetic acid is then completed as described in'the example of'lU.'S. 'PatentNo: r

2,090,941. 7 a v w Example z A saturated solution of potassium" acetatein 94% ethyl alcohol is heated to 80 C., saturated with ammonia under250 lbs. per squareinch pressure, and caused to fiow down aftower incoufitercurrent to a stream of carbondioxide. Thatower is providedwithbubble plates or other devices of the kind commonly used; in theSolvay soda process forpromoting intimate contact between thesolutionand the gas; and capable ofwithstanding a relativelyhighinternal pressure; at its lower end it is provided witha settlingcompartment for the greater part of-the precipitate, the solution beingcontinuously withdrawn from a'level just above the settling compartment.By means of pipes set in the wall thereof the tower is kept-at atemperature of 7 groups.

well as of fatty acids in which one or more hydrogen atoms are replacedby other atoms or Moreover, salts of metals other than alkali metals maybe treated. When treating calcium salts, for' fexample, at temperaturesof the order of 100 C., the bicarbonate first formed breaks down intothe normal carbonate, setting free carbon dioxide for re-use. Thecalcium carbonateis readily separable from the solution by filtration.'l-Iaving described our invention, what we desireto'secure'byLettersPatent is:

80? C., to'which temperature also the solution ispreheated under:pressure before entering the tower. Inside the tower a carbon dioxidepressure of 250' lbs. per square inch is maintained.

'After leaving the tower the solution is allowed to cool and is thenfiltered to separate such bicarbonate as has not been retained in thesettling compartment. The output side of the filter is at atmospheric orlower pressure, and the solutio'n'is forced through, the filter by thecarbon dioxide pressure in the tower. The filtrate is treated to'recover ammonia and. acetic acid therefrom.

Although the inve tion has been described with particular reference tothe treatmentrof alkali metal acetates, it. may 'beapplied to the.treat: ment of salts of homologues of acetic acid as l.- Process for themanufacture of lower fatty acids from their salts with metals selectedfrom the group consisting of alkali metals and alkaline 7 earth metaISwhich comprises bringing carbon dioxide and" ammonia into contact with asolution of the salt so as to form the ammonium salt of the fatty acidand heating the solution of the ammonium salt so obtained to obtain thefree acid therefrom.fg 5 2.; Process for the manufacture of lower] fattyacids from their salts with metals selected from the group consisting ofalkalimetal's and alkaline earth metals, which comprises "brin a carbondioxide and ammonia under pressure intocontact'with a solution of the*salt in an} alcohol so as to form the ammonium salt'ofthe fatt'y acidandheating thesolution of the ammonium salt so obtained to obtain thefree acid therefrom.

3. Process-for the manufacture'of acetic acid from --alkalimetalacetates, which comprises sure of above 70 lbs. per sq. inch'to thesolution so as to 'formthe ammonium salt or the fatty acid and treatingthe solutipn of the ammonium salt so obtainedfto obtain the free acidthere from alkali'metal acetates, which comprises' saturating asdlutionof; the acetate in an "alcohol with ammonia under pressure, passingcarbon dioxide under a partial pressure of above70 155. per sq} inchinto the solution so as to'-' form' ammonium acetatfe and heating theammonium acetate to liberate therefromacetic acid.

.6. Process for-the manufacture of lower-fatty acids from their saltswith metals selecte'd'from the groupconsisting of alkali metals andalkaline earth metals which comprises saturatinga solution ofthe saltwith ammonia under pressure,

thenpassing carbdn-dioxideinto the solution maintained" at atemperatur'e above '70 CIsO as to form the ammonium salt of the'fattyfacid and heating the solution of the'ammonlumsalt so obtained toobtainthe free acid therefrom.

f7. Process for the manufacture or acetic acid from alkali metalacetates, which. comprises saturating a solutionof the acetate in an"alcohol with ammonia under pressure, passing: carbon 'dioxide into thesolution maintained atla temperature above 70'? so as us. form ammoniumacetateqand heatingthe ammonium 1 acetate to liberatetherefrorfiaeticacid;

V 8; Process for the manufacture '6: acetic acld from alkali metalacetates, which comprises saturating a solution of the acetate in analcohol with ammonia under pressure, passing carbon dioxide under apartial pressure of above 70 lbs. per square inch into the solutionmaintained at a temperature between 70 and 130 C. so as to form ammoniumacetate and heating the ammonium acetate to liberate therefrom aceticacid. 9. Process for the manufacture of acetic acid from alkali metalacetates, which comprises saturating a solution of the acetate in analcohol with ammonia under pressure, passing carbon dioxide under apartial pressure of above 70 lbs. per square inch into a solution of theacetate in ethyl alcohol of a concentration between 90 and 98% andmaintained at a temperature between 70 and 130 C. so as to form ammoniumacetate and heating the ammonium acetate to liberate therefrom aceticacid.

10. Process for the manufacture of lower ali- 20 phatic acids from theirsalts with metals selected from the group consisting of alkali metalsand alkaline earth metals which comprises bringing carbon dioxide andammonia into contact with a solution of such a salt in ethyl alcohol of90-98% concentration, so as to form the ammonium'salt of the fatty acid,and heating the solution of the ammonium salt so obtained to obtain thefree acid therefrom.

11. Process for the manufacture of acetic acid from the acetate of ametal selected from the group consisting of the alkali metals and thealkaline earth metals, which comprises bringing carbon dioxide andammonia into contact with a solution of said salt in ethyl alcoholof90-98% concentration, so as to form ammonium acetate, and heating theammonium acetate so obtained to liberate the free acetic acid therefrom.

HENRY DREYFUS. V WALTER HENRY GROOMBRIDGE.

